Previous studies showed that pregnancy rate improves when

Previous studies showed that pregnancy rate improves when ewes have a BCS that exceeds a minimum threshold [43]. The pregnancy rate is increased in sheep with BCS ≥2.5 [44] and >2 [45]. In this work, pregnancy rate was higher in the GnRH group with low BCS compared to the hCG and Control groups. Despite the lack of studies on the relationship between body condition and hormonal treatment in sheep, studies are presented in cows. Administration of hCG on Day 5 or eCG on Day 22 post AI increased conception rate especially in cows with low BCS [46,47]. Several studies have reported a relationship between low BCS and fertility failure, apparently associated with progression of a subsequent pregnancy [48].
Acknowledgment The present study was supported by the Project PNSA 115053 (INTA) and PICT 2012-2238 (FONCyT). The authors thankful to the staff of the Experimental farm Pilcaniyeu of INTA Bariloche for assistance during the study.
Introduction Mammals inhabiting high-latitude regions face critical seasonal fluctuations in climatic conditions and food availability at both the pre- and post-natal life stages. Seasonality is an important factor shaping seasonal ecological adaptations and no sodium salt of life histories in small mammals (Roff, 1992; Stearns, 2000). Seasonal regimes such as photoperiod, temperature and food availability, as well as their combination, generally limit small mammals breeding to more favorable seasons and develop food-hoarding behavior before the coming of harsh winter for maximizing individual's fitness (reproductive success and survival) (Bartke and Steger, 1992; Ebling, 1994). For instance, the effect of photoperiod on seasonal reproduction has been confirmed in wild rodent species. Laboratory studies show that short day (SD) acclimation for 8 to 10 weeks leads to reproductive suppression with decreases in the concentrations of follicle-stimulating hormone (FSH), luteinizing hormone (LH) and testosterone, as well as testis regression in Syrian hamsters (Mesocricetus auratus), Siberian hamsters (Phodopus sungorus) and white-footed mice (Peromyscus leucopus) (Gaston and Menaker, 1967; Greives et al., 2007; Pyter et al., 2005; Revel et al., 2006). Desert hamsters (Phodopus roborovskii) also reduced testes mass in males and the percentage of vaginal opening in females during the 3-month SD acclimation (Zhang et al., 2015). As a potent stimulator, hypothalamic gonadotropin-releasing hormone (GnRH) neurons secrete GnRH into the pituitary to regulate gonadotropin secretion and sexual behavior (Karsch et al., 1997; Herbison, 2006). The seasonal variations in GnRH expression link brain plasticity and fertility. In recent years, studies both in laboratory and wild species show that neurogenesis in some specific brain regions are essential in regulating reproduction and social communication (Hill et al., 2008; Yoon et al., 2005). The studies in laboratory mice and rats show that new cells generated in the subventricular zone (SVZ) lining the lateral ventricles could migrate to olfactory bulb (OB) and influence social recognition between males and females (Feierstein, 2012), the Bruce effect in females after mating (Peretto et al., 2014), and the interactions between a mother and her pups (Furuta and Bridges, 2005; Shingo et al., 2003). Other studies in laboratory and wild rodents and wild chickadees suggest that adult neurogenesis in hippocampal dentate gyrus (DG) and in amygdala (Amy) is associated with learning, memory, social communication and pair bonding (Berson et al., 2002; Freas et al., 2013; Lieberwirth et al., 2012; Snyder et al., 2009). However, there is only a small amount of relevant work with controversial results in ewes (Ovis aries) and meadow voles (Microtus pennsylvanicus) (Galea and Mcewen, 1999; Migaud et al., 2011; Ormerod and Galea, 2003). Further evidence is required to associate adult neurogenesis with seasonal breeding of small mammals.